Process for the recovery of toluene from oils



sept. l1o, 1946.v` c. R. CLARK PROCESS FOR THE RECOVERY OF TOLUENE FROM OILS Filed July 1o, 1945 ATTORNEY Patented Sept. 10, 1946.

UNITED STATES, PATENT OFFICE PROCESS FOR THE REoovERyr OF TOLUENE FROM OILS Charles R. Clark, New York, N. Y., assignor to Allied Chemical & Dye Corporation, New York, N. Y., a corporation of New York Application July.10, 1945, Serial N0. 604,130

Vfron'ims. (ol. 2oz- 42) This invention relates to a process for recovering toluene from mixtures containing it Aand other organic liquids.

This application is a continuation-impart of my co-pending application Serial No. 343,499, iiled July 1,1940.

Numerous hydrocarbon oils are known which contain toluene in varying proportions. For eX- arnple, catalytic treatment of a suitable petroleum fraction in the presence of hydrogen, gives an oil consisting chiefly of hydrocarbons of both aromatic and non-aromatic character, and containing about toluene. Gasoline fractions obtained by the distillation of certain types of petroleum frequently contain substantial proportions of` toluene, although mainly consisting of other hydrocarbons. Oils of petroleum origin having a considerable content of aromatics, including toluene, may be treated by well known selective-solvent processes to produce fractions rich in aroma-tics;A for example, extraction of suitable fractions of such petroleum oils with sulfur dioxide may yield fractions of high toluene content. In such cases toluene is accompanied by non-aromatic oils which may be largely parv aliinic, naphthenic or olefinic in character. A considerable portion of these oils cannot be comN pletely separated from the toluene by direct-fram tional distillation because of the closeness of their boiling points to that of toluene or because .they form constant boiling mixtures with toluene.

Furthermore, while ordinarily toluenevis readily separable by direct fractional distillation from light oils produced by the gasification of coal, in some cases the toluene is accompanied by dilcultly separable non-aromatic oils of the same general character as described, owing to carbonization conditions, type of coal used or other special circumstances. Also synthetic hydrocarbon gas mixtures produced by various catalytic processes may contain toluene which, when recovered, is accompanied by similar ldirliculty separable constituents.

ABy fractional distillation of these oils containing toluene, fractions relatively high in toluene` content may be obtained. These toluene fractions, however, will still contain large amounts of the other constituents. of the oil having boil ing points in the neighborhood of the boiling point of toluene or forming mixtures of constant which toluene distills from the oil. For example, by distillation of the above-described types of oils containing toluene under the most eilcient conditions practicable for rectifying the vapors, a

boiling points in the range 0f temperatures at 2 fraction containing about 82% to 35% toluene appears to represent a product of maximum toluene concentration obtainable by direct fractional distillation. Accordingly, recovery of toluene of a relatively high purity from these sources presents a diiilcultV problem of great industrial im-Y portance.A

For many purposes to which toluene is put, it is desirable to use as pure a material as may be economically available. For example, toluene is largely used for the production of TNT, for which purpose a so-called nitration grade of toluene is now preferred. While toluene products containing substantial proportions of certain hydrocarbon oils other than toluene can be nitrated, the mono-nitro compound vmade from them must be purified prior to complete nitration. This materially increases the cost and complexity of the process for making TNT. Furthermore, even though toluene containing substantial quantities of certain other materials is sometimes used for nitration, this is only because the difficulties of preparing a pure toluene have outweighed the disadvantages of using the impure toluene for the production of explosives. Direct fractional distillation, because of the difliculties pointed out above, Will not eiT'ect a recovery of pure toluene from oils such as enumerated and in many cases will not give fractions of suitably high toluene content or free from materials which even in small concentrations adversely affect the nitration of the toluene or the nitrated product.

It is an object of my invention to provide a process whereby toluene of any desired degree of purity may be recovered from Oils containing it and other hydrocarbons which distill out over the same temperature range as the toluene, which will be referred to as like-boiling, non-aromatic hydrocarbons.

I have now. discovered a relatively pure toluene, accompanied by no more" than 5% of likeboiling, non-aromatic hydrocarbons, can be recovered from many oils containing toluene and other hydrocarbons by an azeotropic distillation of the oil under the conditions hereinafter described.

In using my invention for the treatment of an Oil such as has been described above, containing toluene and other hydrocarbons, particularly when the toluene concentration of the oil is low or the oil is one containing materials of wide boiling range, I prefer first to non-azeotropically fractionally distill the oil (i. e., to fractionally distill the oil in the absence of added azeotropic agent) to recover therefromv an enriched tolu ene fraction which contains, in addition to toluene, other hydrocarbons Which distill at the same temperatures as the toluene. Although toluene fractions having an end boiling point substantially above the boiling point of toluene (e. g. a boiling point Urp to 113 C.) may be azeotropically distilled in the manner hereinafter described, I prefer the toluene fraction recovered in the preliminary non-azeotropic distillation step by one having a maximum boiling point substantially corresponding to the boiling point Vof pure toluene; i. e., 111 C. Further, for the reasons which will be more specifically pointed out below, 1I prefer that the toluene fraction recovered by the preliminary distillation of the crude toluene oil be so cut as to exclude therefrom the forerunnngs which do not contain substantial proportions of toluene, for example to exclude any materials distilling beloW 100 C.

A toluene fraction such as may be obtained by this preliminary distillation, which may contain parafns, naphthenes, or olens, is subjected -to a second distillation in the presence of the methyl, ethyl or butyl ether of ethylene glycol. TheseV materials act as azeotropic agents during the distillation. I have discovered that when one of these materials is mixed With a toluene fraction such as described above and the mixture is subjected to fractional distillation with rectification of the vapors under conditi-ons such vthat a temperature not exceeding a Well dened maximum is maintained at a point in the rectication of the vapors, non-toluene hydrocarbons present in the toluene fraction are distilled from the mixture in the form of their azeotropes with the azeotropic agen-t to leave a residue containing toluene of a desirable high purity with respect to its content of other hydrocarbons originally present in the toluene fraction and not separable from the toluene by direct fractional distillation of the toluene fraction in the absence of the azeotropic agent.

My invention comprises azeotropically distilling a toluene fraction containing hydrocarbons which have similar boiling points to that of the toluene` With rectification of the evolved vapors in the presence of the azeotropic Vagent While maintaining at a point in the rectification of the vapors a temperature not -above the boiling point of the azeotrope Vof toluene and the azeotropic agent (hereinafter referred to as the control temperature), until the unvaporized residue contains at least 95 parts by weight toluene for every 5 parts by weight of said hydrocarbons, which boil from a mixture consisting of toluene and the hydrocarbons in the same temperature range as the toluene boils therefrom. This control temperature will depend upon the azeotropic agent used The following Vtable gives for each material the control temperature at or below which the vapors should be maintained at some point in their rectification when using a given material for the distillation of a toluene fraction:

Regulation of the temperature in the rectication of the vapors to meet the conditions set forth above is accomplished by maintaining an adequate quantity of the azeotropic agent present in the still and/ or rectification column during the distillation of the toluene fraction to selectively carry over through the rectication treatment the vapors of the hydrocarbons to be removed from the toluene. Some of the toluene may also bc carried over., ybut so long as the above temperatures are not exceeded, the undistilled residue will be enriched in toluene and by continuing the distillation, separation of the toluene from the hydrocarbons of similar boiling range will be accomplished.

After the distillation has been carried to the point at which the residue containing toluene has the desired purity with respect to hydrocarbons distilling Vfrom the toluene fraction in the same temperature range as the toluene distille therefrom in the absence of the azeotropic agent, the

distillation may be stopped and the residue Withdrawn from the still. Usually the toluene fraction subjected to azeotropic distillation in practicing this invention will be one having a top boiling point not above 118 C. and preferably not above 111 C. The toluene fraction, therefore, will contain little, if any, hydrocarbons boiling from the fraction at `temperatures above those at which toluene boils therefrom. Accordingly, the residue Withdrawn from the still `ordinarily Will contain toluene and other hydrocarbons in the proportion of or more parts toluene to 5 or less parts of total hydrocarbons other than toluene. It may be puried further, as desired, to remove any azeotropic agent it contains and to remove any other impurities present. When the distillation is carried to the point at Which all of the azeotropic agent has been distilled out of the residue and lthe toluene constitutes substantially 99% or more of the total hydrocarbon content of the residue, the residue, which may be given a conventional treatment, for example, treatment With sulfuric acid and redistillation, is suitable for marketing as a nitration grade toluene of particularly high purity.

Instead of withdrawing the toluene residue from the still, the distillation may be continued and the toluene distilled over and separately collected from the distillate containing the hydrocarbons from which the toluene residue previously has been separated by azeotropic distillation. If azeotropic agent is present during the distillation and collection of the toluene, the azeotrope of toluene may be distilled out. The toluene may be separated in any suitable manner from the toluene azeotrope recovered by distillation, for example by extraction with a liquid which will form separate layers, one containing the toluene and the other containing the azeotropic agent. Water is a suitable liquid for effecting this separation. In the absence of azeotropic agent, in distilling out the toluene the temperature in the rectification column may rise to the boiling point 'of toluene under the conditions prevailing as to pressure, etc.

As stated above, ordinarily the toluene fraction treated in accordance With my invention will contain` little, if any, hydrocarbons distilling from the hydrocarbon-toluene fraction at temperatures above those at which toluene distills therefrom. On the other hand, it is not necessary that such high boiling hydrocarbons always be excluded from the mixture of aaeotropic agent and toluene fraction subjected to distillation in accordance with my invention. For example, one may desire to azeotropically distill a toluene oil from which all high boiling hydrocarbons have not been removed. In that case, the high boiling hydrocarbons may be left with the toluene residue at the conclusion of the azeotropic distillation of the toluene fraction under the conditions set forth above to separate the toluene from the hydrocarbons of similar boiling range. After this separation has been effected, one may then separate the toluene from high Aboiling hydrocarbons present in the residue by fractional distillation in the absence of the azeotropic agent.

My invention will be more particularly illustrated and described vin conjunction with the following example.

The accompanying drawing diagrammatically illustrates an apparatus suitable for carrying out Y the processes of this example.

The apparatus of the drawing comprises a still I provided witha heater 2 and connected with a rectification column 3' and a condenser 4 for the vapors leaving the top of the column. By means Vof valves 5 and 6, condensate flowing from condenser 4 is returned through pipe 'I to the top of column 3 and refluxed in contact with the vapors rising in the column. The other portion of the condensate is withdrawn through pipe 8. Two receivers 9 and Ill are connected to pipe 8 through valve-controlled branch pipes: II and I2 so that the condensate drawn off through pipe B may be divided and distributed as described below to the vtwo receivers.

Receiver IQ is connected by a pipe I3 controlled by valve I4 with a second still I5. Still I5, like still I, is provided with a heaterk I 6, a rectification column II, a condenser I8 and pipes I9 and 29 controlled by valves 2| and 22 for return of determined proportions o-f condensate from condenser I8 to the top of column I'I and withdrawal of another portion of the condensate through pipe 20. Pipe 2D leads to a separator 23 into which water may be introduced from a pipe 24.

In carrying out one embodiment of my invention in the apparatus described above, a liquid hydrocarbon mixture containing about 20% tol uene, 20% of other aromatic hydrocarbons and the remainder substantially consisting of parafiinic and naphthenic hydrocarbons, with only traces of olens, was introduced into still I. This crude toluene material was produced by catalytic treatment of a petroleum distillate in the presence of hydrogen. f

The charge of this hydrocarbon `duced into still I was boiled in the still and the evolved vapors were counter-currently contacted in column 3 with reux from condenser 4, in which the vapors leaving the top of the column were substantially entirely condensed. Most 01"-,y f

the condensate from condenser 4 was returned through valve 5 and pipe I to the top of the column to furnish the reflux for the column, the remaining small portion of the condensate being continuously withdrawn through valve G and pipe 8 and passed into collecting vessel 9. The distillation was conducted under substantially atmospheric pressure; i. e., the pressure in condenser d and at the top of column 3 was substantially atmospheric and the pressure in still I was only.

enough higher to force the vapor through the rectication column to the condenser.

When the vapor temperature in the top of col-- umn 3 reached 109.7 C., the condensate passing through pipe 8 was diverted to vessel I0. The cut taken in vessel I0 included the distilla coming over up to and at a temperature of 110.8 C. at the top` of the column. After this out has -been taken off to vessel I D, the distillation may be discontinued and the residue left in the still withmixture introf drawn therefrom. The cut in vessel 9 contains the low boiling fraction of the original oil. The residue Withdrawn from the still contains the high boiling components of that oil. This fraction and residue may be treated or yused in any desired manner.

Instead of discontinuing the distillation after the desired cutis taken off to vessel I0, the distillation may be continued and the condensate passing forward through pipe 8 collected in a third vessel, not shown in the drawing, While the distillation is continued as long as may be desired. The cuts in vessel 9 and this third vessel contain low and high boiling fractions of the original oil. If the cut taken ofi to the third vessel is limited to one containing substantial proportions of toluene, f

e. g. up to 115 C. or 120 C., this cut may be redis` tilled o-r introduced to still I with a subsequent batch of oil, and the toluene in this cut recovered.

With efcient rectification of the vapors in column 3 during the fractional 'distillation of the crude toluene oiljthe cut collected in vessel I0 contains about '74% by Weight of toluene, as determined by the specific dispersion method for analyzing hydrocarbon oils described in Industrial and Engineering Chemistry, Analytical Edition, vol. l1, page 614, November 15, 1939.

The toluene fraction collected in vessel I is subjected to azeotropic distillation, which represents the second stage of this example. For this purpose the toluene fraction containing '74% toluene was introduced into still I5 together with commercial methyl ether of ethylene glycol. The mixture o-f-methyl ether of ethylene glycol and toluene fraction Was distilled with rectiiication of the vapors in column II and condensation of the vapors: leaving the top of the column in condenser I`8. Most of the condensate was returned through pipe I9 to the top of column II while the remainder was withdrawn through pipe 20 to separator 23. n

Toluene and the methyl ether of ethylene glycol form an azeotrope having a boiling point of 106 C. Azeotropes formed with the methyl ether of ethylene glycol by the hydrocarbons other than toluene present in the toluene 'fraction introduced into still I5 have boiling points sufficiently below that of the toluene azeotrope for them to be preferentially vaporized and by rectification in column I1 to be largely separated from the toluene andany toluene-methyl ether of ethylene glycol azeotrope which is vaporized in still I5 and enters column I1 so long as there-is suflicient methyl ether of ethylene glycol present in the vapor and liquid phases in the rectification column. As pointed out above, the requisite quantity of methyl ether of ethylene glycol to be supplied is that which will maintain thetemperature at apoint in the rectification column, preferably at the top of the column, not above 106 C. In this example the requisite quantity of methyl ether of ethylene glycol is vsupplied in the initial fcharge to the still by introducing about 30 volumes of the methyl ether of ethylene glycol for every volumes of the toluene fraction.. Methyl ether of ethylene glycol is vaporized from the still, enters the rectication column as vapor and in part is returned to the column as liquid in the condensate from condenser I8. If insuicient methyl ether of ethylene glycol is initially introduced in the charge to the still, additional methyl ether of ethylene glycol, sufficient to maintain the requisite temperature in the rectification column, may be supplied as the distillation progresses. This methyl while the azeotropes of the methyl ether of ethyl- .i

ene glycol with the other hydrocarbons are distilled out and are collected in separator 23. The loss of toluene from the still to the condensate drawn off through pipe will depend upon the efficiency with which the vapors are rectied. Efficient rectication is employed in order to keep down this loss of toluene.

in carrying out the process of this example, as the distillation continued the temperature of the vapors at the top of column l'l rose to about 106C C. The toluene content of the oil obtained from the condensate withdrawn through pipe 2l) by Washing the condensate with water to free it of methyl ether of ethylene glycol increased to about 99 At this point the distillation was discontinued. The residue left in still I5 may be Washed with water to remove methyl ether of ethylene glycol. The oil layer which separates from a water-methyl ether of ethylene glycol layer contains about 99% toluene.

By agitating the distillate collected in separator 23 with Water and allowing the liquid to remain quiescent for a short time, it will separate into two layers. The upper layer is an oil containing the non-toluene constituents of the tolu nene fraction originally supplied to still I5 and the portion of the toluene carried over in the distillation. 'This oil may be treated or used as desired. By separately recovering and treating the distillate in two portions, two oil fractions may be obtained; one low in toluene, which may be added to toluene oil distilled in still I, and a second oil fraction high in toluene, for example containing 74% toluene, which may be introduced into the toluene fraction from vessel I0 and redistilled with this fraction in a subsequent distillation in still i5. tillate the toluene it contains may be recovered. The aqueous methyl ether of ethylene glycol layer separated in treating the distillate with Water may be treated in any of the well known manners to recover methyl ether of ethylene glycol therefrom for use in distilling a subsequent batch of toluene fraction. l

The procedure of this example may be employed to recover 95% or purer toluene from the starting hydrocarbon mixture using ethyl ether of ethylene glycol or butyl ether of ethylene glycol as the azeotropic agent in place of the methyl ether of ethylene glycol.

Numerous changes and modications may be made in the above-described processes without departing from my invention. While in the first distillation step of the crude toluene oil it is preferred to take off a toluene fraction having an end boiling point of substantially 111 C. and fractions with a higher end boiling point, such as 118 C.; may be successfully distilled azeotropically to obtain pure toluene, even a larger leeway is permitted in the temperature at which the toluene fraction starts to be taken off; i. e., in the initial boiling point of the toluene fraction. Nevertheless, it is preferred the toluene fraction subjected to azeotropic distillation be one boiling in the range of 100 C. to 111 C. Such a fraction may be distilled in the azeotropic distillation step of my process and pure toluene obtained with a relatively small quantity of azeotropic agent present during the distillation. Pure toluene may be obtained by distilling with By thus reworking the disthe azeotropic agent a toluene fraction boiling, for example, from C. to 118 C., but the quantity of azeotropic agent present in the distillation of the toluene fraction of wider boiling range must be substantially increased as compared with the quantity which sufces for distilling the fraction of the narrower boiling range.

While I have described my process in conjuncion with an example in which the two distillation steps are batch procedures, either or both of these distillations advantageously may be carried out continuously by well known continuous distillation procedures suitable for the fractional distillation of mixtures of two or more liquids.

The minimum ratio of azeotropic agent to the toluene fraction which is suitable for carrying out my invention will vary with the particular agent used, the amount and nature of the hydrocarbon impurities in the toluene fraction, the purity desired in the toluene residue from the distillation, the proportion oi toluene in the original toluene fraction which is to be recovered in the residue from the distillation, and theprocedure used for the azeotropic distillation. The ratios of the above examples are suitable for a batch process carried out according to the procedures of the example. irrespective of the particular batch or continuous procedure used, the quantity of azeotropic agent used in the distillation of hydrocarbons from a given quantity of toluene fraction should be in excess of that which will form azeotropic mixtures with the non-toluene hydrocarbons which are to be vaporized and taken over into the distillate. This quantity of azeotropic agent includes fresh agent introduced into the material being distilled and also any of the azeotropic agent which may be separated from the distillate and. returned continuously or periodically to the still or rectiiication column while the distillation of the toluene fraction is progressing. rlleinperature readings are taken of the vapor at the top of the rectification column and, by supplying additional azeotropic agent when required to prevent this temperature from rising above the boiling point of the toluene azeotrope, an adequate amount of azeotropic agent will be present during the separation of the non-toluene hydrocarbons from the toluene fraction. It is not necessary that this point of control temperature be at the top of the column, although this is a satisfactory point for determining this temperature in the equipment used for fractionating the vapors and condensing the fractionated vapors in the above examples for effective use of the rectication column. One skilled in the distillation art will recognize suitable points for maintaining this control temperature in any other specinc apparatus according to well known distillation principles.

It is, of course, obvious preliminary distillation of a crude toluene oil to obtain a toluene fraction suitable for recovery of toluene therefrom by the azeotrcpic distillation need not be carried out in immediate conjunction with the azeotropic distillation. rlille toluene fraction may be produced in one plant, transported to and treated later in another plant to aueotropically distill it. Nor is my invention limited to any particular procedure for the production oi the toluene fraction. My invention contemplates distilling with the methyl, ethyl or butyl ether of ethylene glycol any oil containing toluene together with other hydrocarbons which, when the oil is distilled, vaporize therefrom in the same temperature range as the toluene and, therefore, are not separable from the spond to the change inthe boiling point of the toluene azeotrope with change in pressure. The temperatures as given in this specification and in the appended claims are corrected temperatures for oner atmosphere pressure (760 mm. of Hg). l

I claim:

1. A process for the treatment of a hydrocarbon fraction containing toluene and non-aromatic hydrocarbons to separate toluene from the nonaromatic hydrocarbons contained therein which ordinarily distill from said hydrocarbon fraction in the same temperature range as toluene distills therefrom which comprises azeotropically distilling said hydrocarbon fraction in the presence of a suicient amount of a material from the group consisting of the methyl, ethyl and butyl ethers of ethylene glycol t0 vaporize the non-aromatic hydrocarbons together with the ether of ethylene glycol thereby leaving a residue substantially enriched in toluene.

2. A process for the treatment of a hydrocarbon fraction having an end boiling point not above 118 C. and containing toluene and nonaromatic hydrocarbons to separate toluene from the non-aromatic hydrocarbons contained therein l0 which ordinarily distillV from said hydrocarbon fraction in the same temperature range as toluene distills therefrom which comprises azeotropically distilling said hydrocarbon fraction in the presence of a sufficient amount of a material from the group consisting of the methyl, ethyl and butyl ethers of ethylene glycol to vaporize the non-aromatic hydrocarbons together With the ether of ethylene glycol thereby leaving toluene in the residue substantially completely separated from the hydrocarbons other than the toluene.

3. A process for the treatment of a hydrocarbon fraction containing toluene and non-aromatic hydrocarbons to separate toluene from the nonaromatic hydrocarbons contained therein Which ordinarily distill from said hydrocarbon fraction in the same temperature range as toluene distills therefrom which comprises azeotropically distilling said hydrocarbon fraction in the presence of a suicient amount of methyl ether of ethylene f glycol to vaporize the non-aromatic hydrocarbons together With the methyl'ether of ethylene glycol thereby leaving a residue substantially enriched in toluene.

4. A process for the treatment of a hydrocarbon fraction containing toluene and non-aromatic hydrocarbons to separate toluene from the nonaromatio hydrocarbons contained therein which ordinarily distill from said hydrocarbon fraction in the same temperature range as toluene distills therefrom which comprises azeotropically distilling said hydrocarbon fraction in the presence of a sufficient amount of methyl ether of ethylene glycol to vaporize the non-aromatic hydrocarbons together With the methyl ether of ethylene glycol thereby leaving toluene in the residue substantially completely separated from the hydrocarbons other than the toluene.

CHARLES R. CLARK. 

